EEG analysis for cognitive interference effects in a Stroop task

The present EEG study investigates neuronal mechanisms underlying stimulus-response interference effects using a Stroop task. Although recent functional MRI studies showed that the anterior cingulate cortex (ACC) is involved in conflict monitoring during the interference, precise temporal characteristics of neuronal responses and their relationships with the actual motor response time(i.e., the time of motor action) are still unclear. For this, we modified the class Stroop task using action colored words with two relevant motor responses; button pressing and pedal stepping. Complex EEG waveforms from 13 subjects and their response times for three experimental conditions (congruent, incongruent, and neutral) with two types of motor responses were analyzed for finding a special event related potential (ERP) for conflict monitoring. In results, we found that a component of the event related potential, which was a negative wave around 200ms after the stimulus onset (N2b), was significantly modulated with the amount of interference and correlated with response time. The N2b was high and response time was slow when the action word stimulus was incongruent with the required response action. Our results implied that the relatively early ERP component, N2b could be detected when a current stimulus meaning is conflict with a required response action and this signal might be useful for other mechanical purposes such as BCI applications.